This invention relates to a paper delivery for a web offset printing press of a type which discharges paper by shiftedly stacking paper by retardation on a low-speed belt, like a sheeter.
A rolled web offset printing press is provided with a folder which cuts the web, which is printed, dried and cooled, to a predetermined length, or folds it in the cross or longitudinal direction of the web.
Heretofore, in this type of folder, the completed signature which is intermittently fed has been dropped one by one between blades of a fan wheel, rotated, and dropped on a delivery conveyor to be discharged in a shiftedly stacked state.
However, in a paper delivery using a fan wheel, because space (paper delivery pitch) between signatures must be set large to put the signatures into the wheel and in turn the transportation speed of the belt must be increased, a high-speed machine has had a problem in that it is difficult to stably drop the signatures between the fan wheel blades. Furthermore, as the machine speed increases, the retardation ratio before the signature enters the fan wheel becomes large, which tends to cause flaws and scratches on the signatures. If the diameter of the fan wheel is increased to decrease the difference between the peripheral speed of the wheel and the feed speed of the signatures in order to prevent the above problem, the device tends to become larger in size.
The inventors formerly invented a paper delivery which utilizes a sheeter to cut the web into cut sheets and stack them, thereby increasing the speed of the folder.
Since, in the above-described paper delivery, signatures are shiftedly stacked by retardation on a low-speed belt and discharged, above the low-speed belt are disposed a snubber for regulating the vertical relative positions of the foregoing signature and following signature to make paper dodging and retarding the signature by snapping the rear end of the signature between the snubber and the low-speed belt, and a braking roller for retarding the signature down to the speed of the low-speed belt to shiftedly stack the signatures. Furthermore, the outlet side of an upper one of a pair of high-speed belts is overlapped above the inlet side of the low-speed belt
Therefore, as the machine speed increases, the signature tends to strongly hit the braking roller resulting in a damage at the front edge, or the signature tends to be strongly nipped instantaneously between the snubber and the low-speed belt resulting in scratch marks at the rear end of the signature. When, to prevent the signature from strongly hitting the braking roller, the braking roller is moved towards the paper delivery direction, paper dodging between signatures becomes impossible resulting in paper jamming, or, when the rear end of the signature is caused not to be nipped in order to eliminate scratching with the snubber, the unretarded signature hits the braking roller resulting in increased damages to the front edge. Consequently, the signatures can be handled at a rate of no more than 600 units per minute even if a best condition is set where no flaws or damages are caused on the signatures.
Furthermore, when the difference in height between the low-speed belt and the upper high-speed belt with increasing machine speed, even if the rear end of the signature is pushed down by the snubber to drop the signature down onto the low-speed belt, the signature tends to move down only partly due to the inertia in association with the high speed, which causes unstable dodging between signatures resulting in paper jamming.